The present invention relates generally to gun barrels, and more specifically to hybrid gun barrels that can be successfully used with modern hotter propellants.
To successfully pierce modern military armor, the exit velocity, or muzzle velocity, of armor piercing shells fired from modern rapid firing Gatling-like guns, such as the GAU-8 aircraft cannon mounted on the U.S. Air Force A-10 Warthog aircraft, needs to be increased from speeds of about 2500 feet per second (fps) to speeds of about 4000 fps. To achieve these increased speeds, much hotter propellants than are now in use need to be used. Unfortunately, the use of hotter propellants causes much more rapid erosion of the breech end of gun barrels, including the barrel forcing cone where the projectile first enters the gun barrel, than is acceptable for use with rapid firing guns. The erosion and wear results in short barrel lives and decreased gun accuracy.
Conventional gun barrels are rifled along almost their entire length, the rifling originating just forward of the forcing cone. Rifling, spiral grooves cut along the inside of the gun barrel, imparts a spin to a projectile that greatly improves the ballistic characteristics and accuracy of the projectile. Optimum ballistic characteristics of a projectile are particularly important for armor piercing shells because, without the stability imparted by rifling, the projectiles may tumble through the air, even though accuracy might still be maintained. A tumbling projectile may strike armor with its side or back instead of its point and then would not penetrate the armor. Even though rifling causes a great deal of friction against the movement of the projectile through the gun barrel, with the use of modern high performance propellants the stability advantages of rifling have outweighed the higher muzzle velocities that might otherwise be obtainable with a smooth bore gun barrel.
To obtain increased muzzle velocity, the prior art has experimented with a variety of hybrid gun barrels having a rifled breech section and a smooth bore muzzle section. The rifled breech section imparts the desirable spin to the projectile while the smooth bore muzzle section provides higher muzzle velocities. Unfortunately, the rifling on the breech section of the gun barrel still experiences unacceptable erosion and wear if used with the hotter propellants necessary to achieve the needed higher muzzle velocities. Further, while the inventors of these prior art hybrid gun barrels have stated that the accuracy of a fully rifled gun barrel is maintained, the ballistic characteristics, particularly the stability, of projectiles fired by these prior art hybrid gun barrels is suspect.
At least one very early prior art hybrid gun barrel, described in U.S. Pat. No. 37,193 to Alsop, instead of trying to obtain for a modern conventional rifle having a rifled gun barrel some of the advantages of a smooth bore rifle, attempted to obtain for the then more conventional smooth bore gun barrels some of the advantages of a rifled gun barrel. This was done by adding a short rifled tip to the end of a smooth bore gun barrel to impart a last minute spin to the projectile, typically a Minie ball. As noted by modern day inventors, and discussed in U.S. Pat. No. 4,660,312 to A'Costa for a rifled gun barrel having a smooth bore muzzle section, the Alsop gun barrel, if used with modern day ammunition for a rifle, would likely explode when the high velocity projectile suddenly struck the rifling at the end of the gun barrel. If used with a modern armor piercing shell having a rotating band made of a separate material from the rest of the projectile, as is more fully described in the Detailed Description, the rotating band would strip off a high velocity projectile when the projectile struck the rifled tip.
Thus it is seen that there is a need for gun barrels which can withstand the use of modern hotter propellants without unacceptable erosion of the breech end of the gun barrel and which retain the accuracy and stability of fully rifled gun barrels.
It is, therefore, a principal object of the present invention to provide a gun barrel that can withstand the use of hotter propellants without unacceptable erosion of the breech end of the gun barrel while still retaining the accuracy and ballistic characteristics of fully rifled gun barrels.
It is a feature of the present invention that it minimizes the forces on rotating bands from high velocity projectiles fired with hotter propellants.
It is another feature of the present invention that its use of a smooth bore for the breech end of a gun barrel makes it particularly adaptable for use with cased telescoped ammunition.
It is an advantage of the present invention that its use of a smooth bore for the breech end of a gun barrel allows the use of a much greater variety of alternative erosion resistant materials and coatings for the breech end than would be possible if the breech end were rifled.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.